Ocean Acidification: Assessment Of pH in the Channel Islands National Park and its Effect on Sea Urchin Fertilization

Ocean acidification, the decline of seawater pH as a direct result of anthropogenic CO₂ dissolving into surface oceans, is expected to affect the marine ecosystem of the Channel Islands National Park and Santa Barbara Coastal LTER. The objectives of this project were two-fold: (1) to deploy two autonomous pH sensors to characterize near-shore pH at Anacapa Island and Santa Cruz Island and, using pH sensor data, (2) to conduct laboratory based experiments testing fertilization of two sea urchin species (Strongylocentrotus purpuratus) and (S. franciscanus) from both sites at two pH levels (8.0, 7.6) and temperatures (14, 18 °C). Here we present the first record of a pH time series in this National Park in order to establish baseline pH levels in the face of future ocean acidification. Over a three-month deployment period, pH ranged from 7.83-8.09 and 7.55 to 8.15 at Anacapa Island and Santa Cruz Island, respectively. Additionally, there was no clear trend of an effect of pH and temperature on the fertilization success. Both species exhibited high fertilization success in all experimental treatments. Although the Channel Islands marine ecosystem already experiences low levels of pH, it appears that sea urchin fertilization is robust to current and future levels of ocean acidification.